The Scroll Messenger

The Scroll Messenger contracts allow for sending arbitrary messages from L1 to L2 or vice versa. This enables executing functions on another chain in a secure and permissionless way. To send a message from L1 to L2, use the messenger smart contract deployed on L1, L1ScrollMessenger. To send a message from L2 to L1, use the contract deployed on L2, L2ScrollMessenger.

Finalizing transactions on L1

Any upcoming transactions from L2 need to be finalized using the relayMessageWithProof function on the Scroll Messenger contract. We call this process “submitting an Execute Withdrawal transaction,” and it is required for both sending arbitrary messages and transferring assets through a gateway or the router. When you use relayMessageWithProof, you’ll have to provide a Merkle inclusion proof showing your transaction is included in the trie of “withdrawal” messages, along with other parameters. Producing this proof and these values can be done locally and permissionlessly, but at the moment, the easiest way to retrieve these parameters is through our backend APIs:

• Scroll Sepolia API: https://sepolia-api-bridge-v2.scroll.io/api/
• Scroll API: https://mainnet-api-bridge-v2.scroll.io/api/

Supply the address of the EOA or contract responsible for initiating the original transaction on L2 to the /claimable endpoint. The API backend will provide you with all the necessary information to successfully conclude the transaction on L1. Take a look at the following example:

https://sepolia-api-bridge.scroll.io/api/claimable?address=0x031407eaaffFB4f1EC2c999bE4477E52C81de3c5&page_size=10&page=1

The API should return your transaction data in the following format:

{
  "errcode": 0,
  "errmsg": "",
  "data": {
    "result": [
      {
        "hash": "0xa476850306d6ee52b127628ded34dcf2343570873cce9c5383bd497db48d4f9b",
        "amount": "",
        "to": "",
        "isL1": false,
        "l1Token": "",
        "l2Token": "",
        "blockNumber": 748,
        "blockTimestamp": null,
        "finalizeTx": {
          "hash": "",
          "amount": "",
          "to": "",
          "isL1": false,
          "blockNumber": 0,
          "blockTimestamp": null
        },
        "claimInfo": {
          "from": "0x031407eaaffFB4f1EC2c999bE4477E52C81de3c5",
          "to": "0x1039057185CFe192d16c03F5656225821A193FD5",
          "value": "0",
          "nonce": "9",
          "batch_hash": "0x49a18d72dbceeb957f918947b532db452c031f528e7e6bf329007066638c5e50",
          "message": "0xa413686200000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000005686f6c6973000000000000000000000000000000000000000000000000000000",
          "proof": "0x69b4ee6cf9a38bed79668ddd347fef2bdff44c3760c9309fa41decfd60202d22ad3228b676f7d3cd4284a5443f17f1962b36e491b30a40b2405849e597ba5fb5b4c11951957c6f8f642c4af61cd6b24640fec6dc7fc607ee8206a99e92410d3079f53171df5c0661d2afe86c4d97b6f34278daf6a0ea9baff5b4fc979d5629a5",
          "batch_index": "93"
        },
        "createdTime": null
      }
    ],
    "total": 1
  }
}

The claimInfo object under the result json returned has all the information needed to execute your transaction on L1. The parameters needed by the relayMessageWithProof are: from, to, value, nonce, message and proof. Supply these to the relayMessageWithProof function on L1 to execute and finalize your transaction on L1.

Messenger API

Please visit the npm library for the complete Scroll contract API documentation.

sendMessage

function sendMessage(
  address target,
  uint256 value,
  bytes calldata message,
  uint256 gasLimit,
  address refundAddress
) external payable;

Sends arbitrary data from one chain to another. It allows us to execute functions cross-chain.

relayMessageWithProof

function relayMessageWithProof(
  address from,
  address to,
  uint256 value,
  uint256 nonce,
  bytes memory message,
  L2MessageProof memory proof
) external;

Relay a L2 => L1 message with message proof.